1. Field of the Invention
The field of the invention relates to medical marking devices for marking the eye prior to surgery, and a method of using a medical marking device to make a incision of a predetermined length and width.
2. Brief Description of the Prior Art
Medical marking devices have been developed for various surgical operations which involve making incisions in the eye. The marking devices are used prior to surgery, and provide markings to assist the surgeons in correctly locating the areas of the eye on which a keratome or other surgical knife is to be employed. Such devices function by leaving depressions in the eye or sets of ink marks. In either case, the markings identify the locations where incisions are to be made and/or sutures are to be placed.
Cataract extraction and lens implantation surgery is a commonly employed procedure. The techniques for performing such surgery have evolved over the years to the point where suturing the wound is often unnecessary. One procedure for conducting cataract surgery involves making an incision through both scleral and corneal tissue. Such a procedure for constructing a self-sealing incision during cataract surgery is described in the literature..sup.1 This procedure involves the use of a marker to create a grid of dots following cautery to allow selection of incision length and location. A perpendicular scleral groove is formed at the appropriate dots, followed by dissection of a scleral tunnel into clear cornea. The incision is complete when the selected keratome enters the anterior chamber. A more recent technique, called the clear corneal approach, is said to offer significant advantages over the above-described scleral approach. Whereas the scleral approach involves an incision through both scleral and corneal tissue, the primary incision is made substantially only through corneal tissue using the clear corneal approach. (The primary incision is used to remove the cataractous lens tissue and insert an intraocular lens.) Also, topical anesthesia may be used when employing the clear coneal approach.
Advantages of the clear corneal approach include faster patient visual recovery, the use of topical anesthesia, no subconjunctival hemorrhage, no cautery, and better refractive results. Selective location of the primary incision has also been said to allow correction for preoperative against-the-rule astigmatism.
The formation of a leak-proof, sutureless incision is desirable whether the scleral or clear corneal approach is employed. The risk of infection is believed to be significantly reduced if leakage can be avoided.
A corneal incision consists essentially of a tunnel created by a scalpel. The tunnel is composed of a "roof" and a "base". A corneal flap is formed at the distal end of the tunnel base. It is this flap that is pressed against the tunnel roof by intraocular pressure that actually seals the incision. A number of ophthalmologists have conducted research in developing the appropriate corneal incision architecture that would provide a reliable, leak-proof seal. The results of this research indicate that the tunnel length (i.e., the distance from the initial entry site to the tip of the corneal flap) is an important factor in determining the sealability of the incision..sup.2 A specific recommendation made by surgeons who have employed the clear corneal approach is to create an incision that has a maximum width to length ratio of about three to two.